Intramolekulare Reaktionen transienter Phosphenium‐ und Arsenium‐Ionen führen zur Bildung isolierbarer 9‐Phospha‐ und 9‐Arsena‐Fluorenium‐Ionen

Kinetically Stabilized Diarylpnictogenium Ions

The newly prepared and fully characterized stibenium and bismuthenium ions [R_ind MesE]⁺ (E=Sb, Bi; R_ind =dispiro[fluorene-9,3'-(1',1',7',7'-tetramethyl-s-hydrindacen-4'-yl)-5',9''-fluorene) were rigorously compared to the previously communicated phosphenium and arsenium ions (E=P, As) as well as the bis(m-terphenyl) pnictogenium ions [(2,6-Mes₂ C₆ H₃ )₂ E]⁺ (E=Sb, Bi). It is demonstrated that the choice of the aryl substituents dramatically effects the molecular structures (e. g. the primary E-C bond lengths) and the electronic structures (e. g. the energy of the LUMOs).

Cationic Carbene Analogues: Donor-Free Phosphenium and Arsenium Ions

Carbenes and their analogues have constantly enthralled chemists with their intriguing reactivity of ambiphilic character stemming from their electronic structures. Phosphenium and arsenium ions are fiercely reactive cationic species, the stabilization of which has been so far achieved in the condensed phase by dispersing the positive charge through electromeric conjugation with at least one electron-rich substituent (frequently amido groups). Although observed in the gas phase, the isolation of dicoordinate phosphenium and arsenium ions lacking such stabilizing ligands has eluded chemists for decades. Herein we show that by judicious choice of aromatic substituents, dicoordinate, donor-free, Lewis-superacidic phosphenium and arsenium ions can be kinetically stabilized. They feature singlet electronic ground states possessing a vacant p-orbital and an electron lone pair with predominantly s-character.

Isolation of an Antiaromatic 9-Hydroxy Fluorenyl Cation

Fluorenyl cations are textbook examples of 4π electron antiaromatic five-membered ring systems. So far, they were reported only as short-lived intermediates generated under superacidic conditions or by flash photolysis. Attempts to prepare a m-terphenyl acylium cation by fluoride abstraction from a benzoyl fluoride gave rise to an isolable 9-hydroxy fluorenyl cation that formed by an intramolecular electrophilic attack at a flanking mesityl group prior to a 1,2-methyl shift and proton transfer to oxygen.